This invention relates to an image compression device which compresses binary image data at high efficiency and high speed.
Since image data tend to become voluminous, it is extremely inefficient to store or transfer them as they are. In order to transmit data of halftone images or newspaper images effectively by a facsimile, there has been used a technology of transmission for pseudo halftone images which represent halftones with the binary data. There have been known as the prior art Modified Huffman Coding method (MH-Method) and Modified-READ method (MR-Method).
Since the binary image data are compressed in a direction of a main scanning in the image compression device using the aforementioned MH-Method or MR-Method, the compression efficiency is low for processing the binary image data having statistical characteristics (such as resolution) that are different between the main and the auxiliary scanning directions. Since the device processed data in the unit of one bit, the speed of encoding is slow, and hence, the conventional compression device cannot realize the compression at high speed.